Small cell activation procedure

ABSTRACT

A method of wireless communication includes configuring a small cell with activation parameters. The activation parameters include a new carrier type having a reduced periodicity. The method also includes configuring a UE with time restricted measurements. The time restricted measurements correspond to the new carrier type and the reduced periodicity. The method further includes receiving small cell signal measurements from the UE and initiating an activation sequence in response to the small cell signal measurements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/748,204, entitled “SMALL CELL ACTIVATION PROCEDURE,” filed on Jun.23, 2015, which is a divisional of U.S. patent application Ser. No.13/830,702, entitled “SMALL CELL ACTIVATION PROCEDURE,” filed on Mar.14, 2013, now U.S. Pat. No. 9,107,056, which claims the benefit under 35U.S.C. § 119(e) to U.S. Provisional Patent Application No. 61/635,288,entitled “RELAY ACTIVATION PROCEDURE,” filed on Apr. 18, 2012, thedisclosures of which are expressly incorporated by reference herein intheir entireties.

The present application is related to U.S. patent application Ser. No.13/830,747, entitled “SMALL CELL ACTIVATION PROCEDURE,” in the names ofDAMNJANOVIC et al., filed on Mar. 14, 2013, the disclosure of which isexpressly incorporated by reference herein in its entirety.

BACKGROUND Field

Aspects of the present disclosure relate generally to wirelesscommunication systems, and more particularly to controlling small cellactivity states.

Background

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power). Examples of such multiple-access technologies includecode division multiple access (CDMA) systems, time division multipleaccess (TDMA) systems, frequency division multiple access (FDMA)systems, orthogonal frequency division multiple access (OFDMA) systems,single-carrier frequency divisional multiple access (SC-FDMA) systems,and time division synchronous code division multiple access (TD-SCDMA)systems.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example of an emergingtelecommunication standard is Long Term Evolution (LTE). LTE is a set ofenhancements to the Universal Mobile Telecommunications System (UMTS)mobile standard promulgated by Third Generation Partnership Project(3GPP). It is designed to better support mobile broadband Internetaccess by improving spectral efficiency, lower costs, improve services,make use of new spectrum, and better integrate with other open standardsusing OFDMA on the downlink (DL), SC-FDMA on the uplink (UL), andmultiple-input multiple-output (MIMO) antenna technology. However, asthe demand for mobile broadband access continues to increase, thereexists a need for further improvements in LTE technology. Preferably,these improvements should be applicable to other multi-accesstechnologies and the telecommunication standards that employ thesetechnologies.

SUMMARY

In one aspect of the present disclosure, a method of wirelesscommunication is disclosed. The method includes configuring a small cellwith activation parameters. The method also includes configuring a userequipment (UE) with time restricted measurements. The method furtherincludes receiving small cell signal measurements from the UE. Themethod also includes initiating an activation sequence in response tothe small cell signal measurements.

In another aspect of the present disclosure, a method of wirelesscommunication is disclosed. The method includes receiving activationparameters. The method also includes detecting a proximity of an activeUE based at least in part on the activation parameters. The methodfurther includes activating with a new carrier type.

Another configuration discloses an apparatus having means forconfiguring a small cell with activation parameters. The apparatus alsoincludes means for configuring a UE with time restricted measurements.The apparatus further includes means for receiving small cell signalmeasurements from the UE. The apparatus also includes means forinitiating an activation sequence in response to the small cell signalmeasurements.

Yet another configuration discloses an apparatus having means forreceiving activation parameters. The apparatus also includes means fordetecting a proximity of an active UE based at least in part on theactivation parameters. The apparatus further includes means foractivating with a new carrier type.

In another configuration, a computer program product for wirelesscommunications in a wireless network having a non-transitorycomputer-readable medium is disclosed. The computer readable medium hasprogram code recorded thereon which, when executed by the processor(s),causes the processor(s) to perform operations of configuring a smallcell with activation parameters. The program code also causes theprocessor(s) to configure a UE with time restricted measurements. Theprogram code further causes the processor(s) to receive small cellsignal measurements from the UE. The program code also causes theprocessor(s) to initiate an activation sequence in response to the smallcell signal measurements.

In another configuration, a computer program product for wirelesscommunications in a wireless network having a non-transitorycomputer-readable medium is disclosed. The computer readable medium hasprogram code recorded thereon which, when executed by the processor(s),causes the processor(s) to perform operations of receiving activationparameters. The program code also causes the processor(s) to detect aproximity of an active UE based at least in part on the activationparameters. The program code further causes the processor(s) to activatewith a new carrier type.

Still yet another configuration discloses a wireless apparatus having amemory and at least one processor coupled to the memory. Theprocessor(s) is configured to configure a small cell with activationparameters. The processor(s) is further configured to configure a UEwith time restricted measurements. The processor(s) is also configuredto receive small cell signal measurements from the UE. The processor(s)is further configured to initiate an activation sequence in response tothe small cell signal measurements.

Another configuration discloses a wireless apparatus having a memory andat least one processor coupled to the memory. The processor(s) isconfigured to receive activation parameters. The processor(s) is alsoconfigured to detect a proximity of an active UE based at least in parton the activation parameters. The processor(s) is further configured toactivate with a new carrier type.

Additional features and advantages of the disclosure will be describedbelow. It should be appreciated by those skilled in the art that thisdisclosure may be readily utilized as a basis for modifying or designingother structures for carrying out the same purposes of the presentdisclosure. It should also be realized by those skilled in the art thatsuch equivalent constructions do not depart from the teachings of thedisclosure as set forth in the appended claims. The novel features,which are believed to be characteristic of the disclosure, both as toits organization and method of operation, together with further objectsand advantages, will be better understood from the following descriptionwhen considered in connection with the accompanying figures. It is to beexpressly understood, however, that each of the figures is provided forthe purpose of illustration and description only and is not intended asa definition of the limits of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present disclosure willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout.

FIG. 1 is a diagram illustrating an example of a network architecture.

FIG. 2 is a diagram illustrating an example of an access network.

FIG. 3 is a diagram illustrating an example of a downlink framestructure in LTE.

FIG. 4 is a diagram illustrating an example of an uplink frame structurein LTE.

FIG. 5 is a diagram illustrating an example of a radio protocolarchitecture for the user and control plane.

FIG. 6 is a diagram illustrating an example of an evolved Node B anduser equipment in an access network.

FIG. 7 is a diagram conceptually illustrating an exemplary systemaccording to an aspect of the present disclosure.

FIG. 8 is a call flow diagram conceptually illustrating an exemplaryprocess according to an aspect of the present disclosure.

FIG. 9 is a call flow diagram conceptually illustrating an exemplaryprocess according to an aspect of the present disclosure.

FIG. 10 is a call flow diagram conceptually illustrating an exemplaryprocess according to an aspect of the present disclosure.

FIG. 11 is a block diagram illustrating a method for activating a smallcell according to an aspect of the present disclosure.

FIG. 12 is a block diagram illustrating differentmodules/means/components in an exemplary apparatus.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with theappended drawings, is intended as a description of variousconfigurations and is not intended to represent the only configurationsin which the concepts described herein may be practiced. The detaileddescription includes specific details for the purpose of providing athorough understanding of the various concepts. However, it will beapparent to those skilled in the art that these concepts may bepracticed without these specific details. In some instances, well-knownstructures and components are shown in block diagram form in order toavoid obscuring such concepts. Moreover, the term “or” is intended tomean an inclusive “or” rather than an exclusive “or.” That is, unlessspecified otherwise, or clear from the context, the phrase, for example,“X employs A or B” is intended to mean any of the natural inclusivepermutations. That is, for example the phrase “X employs A or B” issatisfied by any of the following instances: X employs A; X employs B;or X employs both A and B. In addition, the articles “a” and “an” asused in this application and the appended claims should generally beconstrued to mean “one or more” unless specified otherwise or clear fromthe context to be directed to a singular form.

Aspects of the telecommunication systems are presented with reference tovarious apparatus and methods. These apparatus and methods are describedin the following detailed description and illustrated in theaccompanying drawings by various blocks, modules, components, circuits,steps, processes, algorithms, etc. (collectively referred to as“elements”). These elements may be implemented using hardware, software,or combinations thereof. Whether such elements are implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented with a “processing system”that includes one or more processors. Examples of processors includemicroprocessors, microcontrollers, digital signal processors (DSPs),field programmable gate arrays (FPGAs), programmable logic devices(PLDs), state machines, gated logic, discrete hardware circuits, andother suitable hardware configured to perform the various functionalitydescribed throughout this disclosure. One or more processors in theprocessing system may execute software. Software shall be construedbroadly to mean instructions, instruction sets, code, code segments,program code, programs, subprograms, software modules, applications,software applications, software packages, firmware, routines,subroutines, objects, executables, threads of execution, procedures,functions, etc., whether referred to as software, firmware, middleware,microcode, hardware description language, or otherwise. For clarity,certain aspects of the techniques are described for LTE or LTE-Advanced(LTE-A) (together referred to as “LTE”) and use such LTE terminology inmuch of the description.

FIG. 1 is a diagram illustrating an LTE network architecture 100. TheLTE network architecture 100 may be referred to as an Evolved PacketSystem (EPS) 100. The EPS 100 may include one or more user equipment(UE) 102, an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN)104, an Evolved Packet Core (EPC) 110, a Home Subscriber Server (HSS)120, and an Operator's IP Services 122. The EPS can interconnect withother access networks, but for simplicity those entities/interfaces arenot shown. As shown, the EPS provides packet-switched services, however,as those skilled in the art will readily appreciate, the variousconcepts presented throughout this disclosure may be extended tonetworks providing circuit-switched services.

The E-UTRAN includes the evolved Node B (eNodeB) 106 and other eNodeBs108. The eNodeB 106 provides user and control plane protocolterminations toward the UE 102. The eNodeB 106 may be connected to theother eNodeBs 108 via a backhaul (e.g., an X2 interface). The eNodeB 106may also be referred to as a base station, a base transceiver station, aradio base station, a radio transceiver, a transceiver function, anaccess point, a basic service set (BSS), an extended service set (ESS),or some other suitable terminology. The eNodeB 106 provides an accesspoint to the EPC 110 for a UE 102. Examples of UEs 102 include acellular phone, a smart phone, a session initiation protocol (SIP)phone, a laptop, a personal digital assistant (PDA), a satellite radio,a global positioning system, a multimedia device, a tablet, a netbook, asmartbook, an ultrabook, a video device, a digital audio player (e.g.,MP3 player), a camera, a game console, or any other similar functioningdevice. The UE 102 may also be referred to by those skilled in the artas a mobile station, a subscriber station, a mobile unit, a subscriberunit, a wireless unit, a remote unit, a mobile device, a wirelessdevice, a wireless communications device, a remote device, a mobilesubscriber station, an access terminal, a mobile terminal, a wirelessterminal, a remote terminal, a handset, a user agent, a mobile client, aclient, or some other suitable terminology.

The eNodeB 106 is connected to the EPC 110 via, e.g., an S1 interface.The EPC 110 includes a Mobility Management Entity (MME) 112, other MMEs114, a Serving Gateway 116, and a Packet Data Network (PDN) Gateway 118.The MME 112 is the control node that processes the signaling between theUE 102 and the EPC 110. Generally, the MME 112 provides bearer andconnection management. All user IP packets are transferred through theServing Gateway 116, which itself is connected to the PDN Gateway 118.The PDN Gateway 118 provides UE IP address allocation as well as otherfunctions. The PDN Gateway 118 is connected to the Operator's IPServices 122. The Operator's IP Services 122 may include the Internet,the Intranet, an IP Multimedia Subsystem (IMS), and a PS (packetswitched) Streaming Service (PSS).

FIG. 2 is a diagram illustrating an example of an access network 200 inan LTE network architecture. In this example, the access network 200 isdivided into a number of cellular regions (cells) 202. One or more lowerpower class eNodeBs 208 may have cellular regions 210 that overlap withone or more of the cells 202. A lower power class eNodeB 208 may be aremote radio head (RRH), a femto cell (e.g., home eNodeB (HeNB)), a picocell, or a micro cell. The macro eNodeBs 204 are each assigned to arespective cell 202 and are configured to provide an access point to theEPC 110 for all the UEs 206 in the cells 202. There is no centralizedcontroller in this example of an access network 200, but a centralizedcontroller may be used in alternative configurations. The eNodeBs 204are responsible for all radio related functions including radio bearercontrol, admission control, mobility control, scheduling, security, andconnectivity to the serving gateway 116.

The modulation and multiple access scheme employed by the access network200 may vary depending on the particular telecommunications standardbeing deployed. In LTE applications, OFDM is used on the downlink andSC-FDMA is used on the uplink to support both frequency division duplex(FDD) and time division duplex (TDD). As those skilled in the art willreadily appreciate from the detailed description to follow, the variousconcepts presented herein are well suited for LTE applications. However,these concepts may be readily extended to other telecommunicationstandards employing other modulation and multiple access techniques. Byway of example, these concepts may be extended to Evolution-DataOptimized (EV-DO) or Ultra Mobile Broadband (UMB). EV-DO and UMB are airinterface standards promulgated by the 3rd Generation PartnershipProject 2 (3GPP2) as part of the CDMA2000 family of standards andemploys CDMA to provide broadband Internet access to mobile stations.These concepts may also be extended to Universal Terrestrial RadioAccess (UTRA) employing Wideband-CDMA (W-CDMA) and other variants ofCDMA, such as TD-SCDMA; Global System for Mobile Communications (GSM)employing TDMA; and Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB),IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, and Flash-OFDMemploying OFDMA. UTRA, E-UTRA, UMTS, LTE, and GSM are described indocuments from the 3GPP organization. CDMA2000 and UMB are described indocuments from the 3GPP2 organization. The actual wireless communicationstandard and the multiple access technology employed will depend on thespecific application and the overall design constraints imposed on thesystem.

The eNodeBs 204 may have multiple antennas supporting MIMO technology.The use of MIMO technology enables the eNodeBs 204 to exploit thespatial domain to support spatial multiplexing, beamforming, andtransmit diversity. Spatial multiplexing may be used to transmitdifferent streams of data simultaneously on the same frequency. The datasteams may be transmitted to a single UE 206 to increase the data rateor to multiple UEs 206 to increase the overall system capacity. This isachieved by spatially precoding each data stream (i.e., applying ascaling of an amplitude and a phase) and then transmitting eachspatially precoded stream through multiple transmit antennas on thedownlink. The spatially precoded data streams arrive at the UE(s) 206with different spatial signatures, which enables each of the UE(s) 206to recover the one or more data streams destined for that UE 206. On theuplink, each UE 206 transmits a spatially precoded data stream, whichenables the eNodeB 204 to identify the source of each spatially precodeddata stream.

Spatial multiplexing is generally used when channel conditions are good.When channel conditions are less favorable, beamforming may be used tofocus the transmission energy in one or more directions. This may beachieved by spatially precoding the data for transmission throughmultiple antennas. To achieve good coverage at the edges of the cell, asingle stream beamforming transmission may be used in combination withtransmit diversity.

In the detailed description that follows, various aspects of an accessnetwork will be described with reference to a MIMO system supportingOFDM on the downlink. OFDM is a spread-spectrum technique that modulatesdata over a number of subcarriers within an OFDM symbol. The subcarriersare spaced apart at precise frequencies. The spacing provides“orthogonality” that enables a receiver to recover the data from thesubcarriers. In the time domain, a guard interval (e.g., cyclic prefix)may be added to each OFDM symbol to combat inter-OFDM-symbolinterference. The uplink may use SC-FDMA in the form of a DFT-spreadOFDM signal to compensate for high peak-to-average power ratio (PAPR).

FIG. 3 is a diagram 300 illustrating an example of a downlink framestructure in LTE. A frame (10 ms) may be divided into 10 equally sizedsub-frames. Each sub-frame may include two consecutive time slots. Aresource grid may be used to represent two time slots, each time slotincluding a resource block. The resource grid is divided into multipleresource elements. In LTE, a resource block contains 12 consecutivesubcarriers in the frequency domain and, for a normal cyclic prefix ineach OFDM symbol, 7 consecutive OFDM symbols in the time domain, or 84resource elements. For an extended cyclic prefix, a resource blockcontains 6 consecutive OFDM symbols in the time domain and has 72resource elements. Some of the resource elements, as indicated as R 302,R 304, include downlink reference signals (DL-RS). The DL-RS includeCell-specific RS (CRS) (also sometimes called common RS) 302 andUE-specific RS (UE-RS) 304. UE-RS 304 are transmitted only on theresource blocks upon which the corresponding physical downlink sharedchannel (PDSCH) is mapped. The number of bits carried by each resourceelement depends on the modulation scheme. Thus, the more resource blocksthat a UE receives and the higher the modulation scheme, the higher thedata rate for the UE.

FIG. 4 is a diagram 400 illustrating an example of an uplink framestructure in LTE. The available resource blocks for the uplink may bepartitioned into a data section and a control section. The controlsection may be formed at the two edges of the system bandwidth and mayhave a configurable size. The resource blocks in the control section maybe assigned to UEs for transmission of control information. The datasection may include all resource blocks not included in the controlsection. The uplink frame structure results in the data sectionincluding contiguous subcarriers, which may allow a single UE to beassigned all of the contiguous subcarriers in the data section.

A UE may be assigned resource blocks 410 a, 410 b in the control sectionto transmit control information to an eNodeB. The UE may also beassigned resource blocks 420 a, 420 b in the data section to transmitdata to the eNodeB. The UE may transmit control information in aphysical uplink control channel (PUCCH) on the assigned resource blocksin the control section. The UE may transmit only data or both data andcontrol information in a physical uplink shared channel (PUSCH) on theassigned resource blocks in the data section. An uplink transmission mayspan both slots of a subframe and may hop across frequency.

A set of resource blocks may be used to perform initial system accessand achieve uplink synchronization in a physical random access channel(PRACH) 430. The PRACH 430 carries a random sequence and cannot carryany uplink data/signaling. Each random access preamble occupies abandwidth corresponding to six consecutive resource blocks. The startingfrequency is specified by the network. That is, the transmission of therandom access preamble is restricted to certain time and frequencyresources. There is no frequency hopping for the PRACH. The PRACHattempt is carried in a single subframe (1 ms) or in a sequence of fewcontiguous subframes and a UE can make only a single PRACH attempt perframe (10 ms).

FIG. 5 is a diagram 500 illustrating an example of a radio protocolarchitecture for the user and control planes in LTE. The radio protocolarchitecture for the UE and the eNodeB is shown with three layers: Layer1, Layer 2, and Layer 3. Layer 1 (L1 layer) is the lowest layer andimplements various physical layer signal processing functions. The L1layer will be referred to herein as the physical layer 506. Layer 2 (L2layer) 508 is above the physical layer 506 and is responsible for thelink between the UE and eNodeB over the physical layer 506.

In the user plane, the L2 layer 508 includes a media access control(MAC) sublayer 510, a radio link control (RLC) sublayer 512, and apacket data convergence protocol (PDCP) 514 sublayer, which areterminated at the eNodeB on the network side. Although not shown, the UEmay have several upper layers above the L2 layer 508 including a networklayer (e.g., IP layer) that is terminated at the PDN gateway 118 on thenetwork side, and an application layer that is terminated at the otherend of the connection (e.g., far end UE, server, etc.).

The PDCP sublayer 514 provides multiplexing between different radiobearers and logical channels. The PDCP sublayer 514 also provides headercompression for upper layer data packets to reduce radio transmissionoverhead, security by ciphering the data packets, and handover supportfor UEs between eNodeBs. The RLC sublayer 512 provides segmentation andreassembly of upper layer data packets, retransmission of lost datapackets, and reordering of data packets to compensate for out-of-orderreception due to hybrid automatic repeat request (HARQ). The MACsublayer 510 provides multiplexing between logical and transportchannels. The MAC sublayer 510 is also responsible for allocating thevarious radio resources (e.g., resource blocks) in one cell among theUEs. The MAC sublayer 510 is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE andeNodeB is substantially the same for the physical layer 506 and the L2layer 508 with the exception that there is no header compressionfunction for the control plane. The control plane also includes a radioresource control (RRC) sublayer 516 in Layer 3 (L3 layer). The RRCsublayer 516 is responsible for obtaining radio resources (i.e., radiobearers) and for configuring the lower layers using RRC signalingbetween the eNodeB and the UE.

FIG. 6 is a block diagram of an eNodeB 610 in communication with a UE650 in an access network. In the downlink, upper layer packets from thecore network are provided to a controller/processor 675. Thecontroller/processor 675, e.g., implements the functionality of the L2layer. In the downlink, the controller/processor 675 provides headercompression, ciphering, packet segmentation and reordering, multiplexingbetween logical and transport channels, and radio resource allocationsto the UE 650 based on various priority metrics. Thecontroller/processor 675 is also responsible for HARQ operations,retransmission of lost packets, and signaling to the UE 650.

The TX processor 616, e.g., implements various signal processingfunctions for the L1 layer (i.e., physical layer). The signal processingfunctions includes coding and interleaving to facilitate forward errorcorrection (FEC) at the UE 650 and mapping to signal constellationsbased on various modulation schemes (e.g., binary phase-shift keying(BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying(M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded andmodulated symbols are then split into parallel streams. Each stream isthen mapped to an OFDM subcarrier, multiplexed with a reference signal(e.g., pilot) in the time and/or frequency domain, and then combinedtogether using an Inverse Fast Fourier Transform (IFFT) to produce aphysical channel carrying a time domain OFDM symbol stream. The OFDMstream is spatially precoded to produce multiple spatial streams.Channel estimates from a channel estimator 674 may be used to determinethe coding and modulation scheme, as well as for spatial processing. Thechannel estimate may be derived from a reference signal and/or channelcondition feedback transmitted by the UE 650. Each spatial stream isthen provided to a different antenna 620 via a separatetransmitter/modulator 618TX. Each transmitter 618TX modulates an RFcarrier with a respective spatial stream for transmission.

At the UE 650, each receiver/demodulator 654RX receives a signal throughits respective antenna 652. Each receiver 654RX recovers informationmodulated onto an RF carrier and provides the information to thereceiver (RX) processor 656. The RX processor 656 implements varioussignal processing functions of the L1 layer. The RX processor 656performs spatial processing on the information to recover any spatialstreams destined for the UE 650. If multiple spatial streams aredestined for the UE 650, they may be combined by the RX processor 656into a single OFDM symbol stream. The RX processor 656 then converts theOFDM symbol stream from the time-domain to the frequency domain using aFast Fourier Transform (FFT). The frequency domain signal comprises aseparate OFDM symbol stream for each subcarrier of the OFDM signal. Thesymbols on each subcarrier, and the reference signal, is recovered anddemodulated by determining the most likely signal constellation pointstransmitted by the eNodeB 610. These soft decisions may be based onchannel estimates computed by the channel estimator 658. The softdecisions are then decoded and deinterleaved to recover the data andcontrol signals that were originally transmitted by the eNodeB 610 onthe physical channel. The data and control signals are then provided tothe controller/processor 659.

The controller/processor 659, e.g., implements the L2 layer. Thecontroller/processor can be associated with a memory 660 that storesprogram codes and data. The memory 660 may be referred to as acomputer-readable medium. In the uplink, the controller/processor 659provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the core network. The upper layerpackets are then provided to a data sink 662, which represents all theprotocol layers above the L2 layer. Various control signals may also beprovided to the data sink 662 for L3 processing. Thecontroller/processor 659 is also responsible for error detection usingan acknowledgement (ACK) and/or negative acknowledgement (NACK) protocolto support HARQ operations.

In the uplink, a data source 667 is used to provide upper layer packetsto the controller/processor 659. The data source 667 represents allprotocol layers above the L2 layer. Similar to the functionalitydescribed in connection with the downlink transmission by the eNodeB610, the controller/processor 659 implements the L2 layer for the userplane and the control plane by providing header compression, ciphering,packet segmentation and reordering, and multiplexing between logical andtransport channels based on radio resource allocations by the eNodeB610. The controller/processor 659 is also responsible for HARQoperations, retransmission of lost packets, and signaling to the eNodeB610.

Channel estimates derived by a channel estimator 658 from a referencesignal or feedback transmitted by the eNodeB 610 may be used by the TXprocessor 668 to select the appropriate coding and modulation schemes,and to facilitate spatial processing. The spatial streams generated bythe TX processor 668 are provided to different antenna 652 via separatetransmitters/modulators 654TX. Each transmitter 654TX modulates an RFcarrier with a respective spatial stream for transmission.

The uplink transmission is processed at the eNodeB 610 in a mannersimilar to that described in connection with the receiver function atthe UE 650. Each receiver/demodulator 618RX receives a signal throughits respective antenna 620. Each receiver 618RX recovers informationmodulated onto an RF carrier and provides the information to a RXprocessor 670. The RX processor 670, e.g., may implement the L1 layer.

The controller/processor 675, e.g., implements the L2 layer. Thecontroller/processor 675 can be associated with a memory 676 that storesprogram codes and data. The memory 676 may be referred to as acomputer-readable medium. In the uplink, the controller/processor 675provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the UE 650. Upper layer packets fromthe controller/processor 675 may be provided to the core network. Thecontroller/processor 675 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations. Thecontroller/processor 675 and the controller/processor 659 may direct theoperation at the eNodeB 610 and the UE 650, respectively. Thecontroller/processor 675 or other processors and modules at the eNodeB610 may perform or direct the execution of various processes for thetechniques described herein. The controller/processor 659 or otherprocessors and modules at the UE 650 may also perform or direct theexecution of various processes for the techniques described herein. Thememory 676 and the memory 660 may store data and program codes for theeNodeB 610 and the UE 650, respectively.

Although the description of FIG. 6 is with respect to the eNodeB 610 andthe UE 650, when a small cell is involved, either the apparatus 610 or650 can be a small cell. For example, if UE to small cell communicationsare considered, the small cell corresponds to the apparatus 610, and ifsmall cell to eNodeB communications are considered, the small cellcorresponds to the apparatus 650.

FIG. 7 illustrates an exemplary network structure 700. The exemplarynetwork structure 700 may include one or more of a terminal or UE 702, asmall cell, relay station, or UeNodeB (UeNB) 706, and a donor eNodeB(DeNB) 710. The UE 702 and UeNB 706 may communicate via an access link704. Furthermore, the UeNB 706 and eNodeB 710 may communicate via abackhaul link 708. The eNodeB 710 may also be connected to the backendof the network 712. The backend of the network 712 may include agateway, the internet, and the network core. The small cell may comprisea relay or relay station, an eNodeB, or a UE. The small cell may be alow power node with either a wired or wireless backhaul link.

Aspects of the present disclosure are directed to a small cellactivation procedure. More specifically, aspects of the presentdisclosure are directed to activating small cells based on uplink (UL)transmissions. The uplink transmissions may be physical uplink channeltransmissions and may include a random access channel transmission, suchas a physical random access channel (PRACH) signature sequence, areference signal, such as a sounding reference signal (SRS), or anotheruplink channel.

In another aspect of the present disclosure, the small cell may beactivated to use new carrier type (NCT) downlink transmissions from thesmall cell. The new carrier type specifies that a common referencesignal is not transmitted in all subframes and a frequency of otheroverhead channels, such as a primary synchronization signal (PSS), asecondary synchronization signal (SSS), and a physical broadcast channel(PBCH), is reduced. By transmitting overhead signals at a reducedperiodicity (e.g., according to the NCT configuration), overhead signalpollution will be reduced.

When a small cell is activated, a UE may be configured to measure thesignal from the small cell on subframes when macro and pico eNodeBs areconfigured with almost blank subframes. Additionally, UEs may useinterference cancellation to detect signals from eNodeBs, detect smallcells, perform measurements, report the measurements to the network(e.g., a serving cell such as a macro or pico eNodeB), or a combinationthereof.

FIG. 8 illustrates an exemplary call flow diagram for a small cellactivation procedure. In one configuration, the donor eNodeB 830 mayinclude or be coupled to a radio resource management (RRM) server 805.As shown in FIG. 8, at time T1, the donor eNodeB 830 may configure thesmall cell 810 with activation parameters. For example, the small cell810 is informed of where to search for the UE 820. The activationparameters may indicate a physical random access channel (PRACH)signature sequence space, time/frequency resources, or other uplinktransmission signal parameters. The activation parameters may alsoinclude an offset specific to the small cell. By transmitting overheadsignals with the offset, a UE can distinguish transmissions fromdifferent small cells. In another configuration, there is no offset orall small cells have the same offset.

At time T2, the small cell 810 may be activated to transmit a newcarrier type (NCT) based on the activation parameters. For example, theactivation parameters may configure the small cell 810 to transmitdownlink overhead signals with a reduced periodicity. The periodicitycan be reduced if radio conditions are satisfied, for example, if theradio conditions are good. The downlink overhead signals may includesynchronization signals, such as the primary synchronization signal(PSS) and secondary synchronization signal (SSS), a broadcast channelsignal, such as a physical broadcast channel (PBCH), or a combinationthereof. After being configured with the activation parameters, thesmall cell 810 may transmit the downlink signals (not shown). Thus, theUE 820 can detect the small cell 810.

Furthermore, at time T3, the UE 820 is configured to measure downlinktransmissions from the small cell 810. That is, the UE 820 is made awareof the periodicity and offset configuration of the small cell. In oneconfiguration, the UE 820 may be configured with restricted resourcemeasurements (e.g., using one of n subframes for measurements). Upondetecting the downlink transmissions from the small cell, at time T4,the UE 820 transmits the measurements to the network. Finally, at timeT5, the donor eNodeB 830 may activate the small cell 810 based on themeasurements received from the UE.

As shown in FIG. 8, at time T1, the donor eNodeB may define small cellactivation procedures. The activation procedures may or may not rely onproximity detection of UEs. In one configuration, N-subframes and a newcarrier type (NCT) may be specified for resource restrictedmeasurements. In another configuration, almost blank subframes (ABSs)for pico cells may be specified. Currently, almost blank subframes arenot specified for pico cells.

In yet another configuration, a new LTE carrier type may be specifiedwhere a common reference signal (CRS) is not present in all subframes.In still yet another configuration, a flexible configuration for channelstate information reference signal (CSI-RS) ports may be specified toaddress a dense small cell deployment. A dense small cell deployment mayrefer to a scenario when a large number of active small cells arepresent in small geographical area. The small cells in the densedeployment may be configured to transmit CRS/CSI-RS during macro/picoalmost blank subframes to allow UEs to detect these small cells.

The small cell may be configured to transmit overhead signals. In oneconfiguration the overhead signals are transmitted in specificsubframes, such as subframes 0/5. In another configuration the overheadsignals are transmitted at a lower duty cycle. The small cell mayoperate in a new carrier type mode such that the overhead signals aretransmitted at a lower duty cycle. In one configuration, transmission ofreference signals, such as a common reference signal or a channel stateinformation reference signal, may span multiple measurement instances(e.g., five bursts in 200 ms, spaced apart every 40 ms).

Typically, each small cell may transmit the overhead signals orreference signals with a configurable periodicity. That is, each smallcell may have a separate configuration. The periodicity of the overheadsignals and the reference signals may be reduced in comparison to atypical LTE schedule, such as the schedule of LTE Release 11. Accordingto one configuration, pseudo random transmissions may be specified forthe transmissions of the overhead signals or reference signals.

In one configuration, the small cell activation may be networkcontrolled. That is, as shown in FIG. 8, UEs may detect small cells andreport measurements to the donor eNodeB. The donor eNodeB may activatespecific small cells based on reports received from one or more UEs.Still, in another configuration, the small cell activation may beautonomous.

FIG. 9 illustrates an exemplary call flow diagram for defining anautonomous small cell activation procedure using UE transmissionsaccording to an aspect of the present disclosure. As illustrated in FIG.9, in one configuration, the donor eNodeB 930 may include a radioresource management (RRM) server 905. In another configuration, thedonor eNodeB 930 may be coupled to the RRM server 905. At time T1, thedonor eNodeB 930 may configure the small cell 910 with activationparameters. The activation parameters may indicate physical uplinktransmissions of a UE 920. Specifically, the small cell 910 may useactivation parameters included in the physical uplink transmissions todetect a UE's proximity. The physical uplink transmissions may includerandom access channel transmissions, such as a physical random accesschannel signature sequence, or reference signals, such as a soundingreference signal.

In one configuration, the donor eNodeB 930 may trigger the UE 920 totransmit on the physical uplink channel. For example, at time T2, thedonor eNodeB 930 may transmit a control channel order, such as aphysical downlink control channel (PDCCH) order, to trigger a randomaccess channel transmission or a reference signal transmission from theUE 920. Alternatively, the uplink transmission may be semi-staticallyconfigured.

In response to receiving the uplink trigger or semi-staticconfiguration, at time T3, the UE 920 may transmit a signal, such as therandom access channel transmission or a reference signal transmission.At time T4, the small cell 910 may detect the uplink transmission fromthe UE. If the uplink transmission satisfies thresholds, such as uplinkthreshold values provided in the activation parameters, the small cell910 may initialize autonomous activation. In one configuration, thesmall cell 910 may be activated with a reduced periodicity. In anotherconfiguration, the small cell 910 may be activated with the reducedperiodicity of the new carrier type.

According to another configuration, the UE only transmits the randomaccess channel signature sequence and does not continue with the randomaccess procedure. That is, the UE does not monitor for a random accessresponse from the donor eNodeB. This may be achieved with an uplinktrigger, such as a downlink control channel order, or without an uplinktrigger so that the transmission is periodic (e.g., periodic randomaccess channel based sounding). According to another configuration, thedonor eNodeB does not proceed with the typical random access channelprocedure in response to receiving the random access channeltransmission from the UE. The random access channel transmission may betransmitted with full transmit power or with a power level determined bya power control algorithm towards the serving cell that triggered randomaccess channel transmission.

For example, in FIG. 9, as previously discussed, the donor eNodeB 930may transmit a control channel order to trigger a random access channeltransmission or a reference signal transmission from the UE 920. Inresponse to receiving the uplink trigger or semi-static configuration,at time T3, the UE 920 transmits a signal, such as the random accesschannel transmission or a reference signal transmission. In oneconfiguration, the random access channel transmission of the UE 920 doesnot trigger the typical random access channel procedure at the donoreNodeB 930.

FIG. 10 illustrates an exemplary call flow diagram for defining anautonomous small cell activation procedure according to an aspect of thepresent disclosure. As illustrated in FIG. 10, the donor eNodeB 1030 mayinclude or be coupled to a radio resource management server 1005. Attime T1, the donor eNodeB 1030 may configure the small cell 1010 withactivation parameters. The activation parameters may indicate physicaluplink transmissions, such as a random access channel transmission or areference signal transmission, of a UE 1020. Specifically, the smallcell 1010 may use activation parameters included in the physical uplinktransmissions to detect a UE's proximity.

In one configuration, the donor eNodeB 1030 may trigger the UE 1020 totransmit on the physical uplink channel. For example, the donor eNodeB1030 may transmit a control channel order, such as a PDCCH order, attime T2, to trigger the transmission of a signature sequence, such as aPRACH signature sequence, or reference signal, such as a SRS, from theUE 1020. Alternatively, the uplink transmission may be semi-staticallyconfigured.

In response to receiving the uplink trigger or a semi-staticconfiguration, the UE 1020 may transmit a signal, such as the signaturesequence or the reference signal, on a physical channel at time T3. Attime T4, the small cell 1010 may detect the transmission from the UE. Ifthe uplink transmission from the UE 1020 is equal to or greater than athreshold, such as uplink threshold values provided in the activationparameters, the small cell 1010 may begin autonomous activation. In oneconfiguration, the small cell 1010 is activated with a first reducedperiodicity. In another configuration, the small cell 1010 may also beactivated with the new carrier type.

Moreover, at time T5, after being activated with a reduced periodicity,the small cell 1010 may initiate network activation. Specifically, thesmall cell 1010 may transmit an activation request to the donor eNodeB1030. The activation request may include the detected measurements ofuplink transmissions from the UE. In response to receiving theactivation request, at time T6, the donor eNodeB 1030 may transmit anactivation grant to the small cell 1010. The activation grant mayactivate the small cell with a second periodicity, at time T7. Thesecond periodicity may be a full periodicity. According to oneconfiguration, the small cell 1010 may bypass the activation at time T4and proceed to network activation at time T5.

As discussed above, according to one aspect of the present disclosure,the donor eNodeB may configure the small cell to detect specificactivation parameters. The activation parameters may enable the smallcell to detect the UE's proximity. These parameters may include randomaccess channel transmissions, time/frequency resources, referencesignals, or other uplink transmissions. For random access channeltransmissions parameters, such as a physical random access channelparameter, the small cell may be configured based on the physical randomaccess channel configuration of a serving cell. Furthermore, in oneconfiguration, the small cell may also be configured based on thephysical random access channel configuration of one or more neighboringcells. The activation parameters may also include threshold values. Forexample, the threshold value may include a minimum signal strength. Thatis, when the detected signal strength of a UE is above the threshold,the small cell may be activated because the UE is within a specificdistance from the small cell. In another configuration, the thresholdsmay include an interference threshold.

As illustrated in FIGS. 9 and 10, the donor eNodeB may dynamicallytrigger the UE to transmit a reserved set of signature sequences, timeresources, frequency resources, or a combination thereof, via an uplinksignal. The triggering may be based on criteria observed by the donoreNodeB, such as data load or radio conditions. For example, the donoreNodeB may only transmit the uplink trigger for UEs with a high downlinkdata load and when the network is loaded. Alternatively, the donoreNodeB may semi-statically configure a periodic or event based triggerfor uplink transmissions during network setup.

In one configuration, the network may transmit an activation grant inresponse to receiving the activation request from the small cell. Inthis configuration, the RRM server may determine that a group of smallcells have detected the same UE. Typically, multiple small cells are notactivated for the same UE. Thus, the RRM server may transmit theactivation request to other RRM servers associated with neighboringdonor eNodeBs to coordinate the activation grants. Alternatively,according to another configuration, one RRM server may be associatedwith multiple donor eNodeBs, and therefore, the RRM server does notcoordinate with other RRM servers. The small cell may be activated andstart a power ramp up procedure after receiving the activation grant.

Upon activation of a small cell, the small cell may be configured totransmit overhead signals that are different from the overhead signalsused by the donor eNodeB. In another configuration, the overhead signalsused by the small cell may be the same as the overhead signals used bythe donor eNodeB. When the overhead signals used by the small cell arethe same as the overhead signals of the donor eNodeB, the small cell mayappear as the same cell as the donor eNodeB. Moreover, when the overheadsignals are different from the overhead signals of the eNodeB, the smallcell may appear as a different cell. Furthermore, when the overheadsignals of the small cell and the eNodeB are the same, the small cellmay have a unique global cell ID. Alternatively, the small cell may havea global cell ID that is the same as the donor eNodeB's global cell ID.Furthermore, the small cell may have different configured antenna ports.In the latter scenario, the small cell may appear as an extension of adonor eNodeB. In one configuration, unique CSI-RS ports (e.g., CSI-portsthat are different from donor eNodeB and neighboring UE small cells) maybe configured for the purpose of radio resource management and channelstate information feedback. If CSI-RS transmissions are configured to bedifferent for each small cell, it becomes less likely that resourceswill collide.

As previously discussed, according to one configuration, a network mayconfigure a small cell station with activation parameters. Theactivation parameters may include uplink parameters for detecting a UE.In another configuration, the activation parameters may include downlinkparameters, such as downlink radio conditions for determining whether asignal strength, interference, or a combination thereof, is within athreshold. That is, the downlink parameters may include a referencesignal received power (RSRP), reference signal received quality (RSRQ),or signal to interference plus noise ratio (SINR). The small cell may beactivated when downlink parameters meet a threshold. In oneconfiguration, the activation parameters may only include the downlinkparameters. Alternatively, the activation parameters may include boththe downlink parameters and the uplink parameters.

Furthermore, in another configuration, the network may configure thesmall cell station to transmit downlink overhead signals with a reducedperiodicity and a subframe/resource block offset, O_tf_1. In oneconfiguration, the reduced periodicity may be infinity. That is, thereduced periodicity may effectively equal zero transmissions. Thedownlink overhead signals may include a primary synchronization signal,a secondary synchronization signal, a physical broadcast channel, or acombination thereof.

As previously discussed, the UE may detect the transmitted downlinkoverhead signals and may transmit the detected measurements to the donoreNodeB. In one configuration, the small cell may use the new carriertype. Furthermore, in another configuration, the small cell may transmitdownlink overhead signals even if the small cell does not detect a UE.In yet another configuration, because many small cells may be detectedby the UE, each small cell may have a different offset to distinguishthe small cells.

Moreover, in still yet another configuration, the overhead signaltransmissions of the small cell may be the same as overhead signaltransmissions of the donor eNodeB in order to obtain a single frequencynetwork (SFN) effect for time/frequency tracking. In this case, theoffset is the same for all small cells. Alternatively, the overheadsignal transmissions of the small cell may be different from theoverhead signal transmissions of the donor eNodeB. In one configuration,when CSI-RS transmissions are configured for a small cell, overheadsignal transmissions may be different for each small cell station.Furthermore, in one configuration, the interference measurement report(IMR) resources may also be different for each small cell station.

Moreover, in one configuration, a UE may be configured to measuredownlink transmissions from the small cell. The UE may be aware of thetransmission periodicity and offset if the small cell is configured forreduced transmission with such offset. Furthermore, the UE may beconfigured with restricted measurements. That is, for example, the UEmay be configured to use one subframe out of n subframes for thedownlink transmission measurements.

As illustrated in FIGS. 9 and 10, at time T2, the donor eNodeB maydynamically or semi statically trigger uplink transmissions from the UEfor uplink sounding purposes. Furthermore, at time T3, a UE may transmituplink signals as configured/triggered by donor eNodeB. Additionally, ifthe small cell detects the uplink transmissions at time T4, the smallcell may change its periodicity and offset. For example, the offset maybe O_tf_2 and the periodicity may be infinity. That is, the periodicitymay effectively equal zero transmissions. In one configuration, thechanging of the periodicity and offset of time T4 may be optional in thecall flow of FIG. 8. In another configuration, the small cell mayautonomously activate upon detecting the uplink transmission from theUE.

As illustrated in FIG. 10, in one configuration, at time T5, the smallcell may transmit an activation request to the donor eNodeB or radioresource management server when the small cell detects an uplink signalfrom a UE. The activation request may include an uplink signalmeasurement report that includes a measurement object, such as a randomaccess channel transmission or a reference signal. The activationrequest may also include other measurement attributes, such as adeselected sequence, signal strength, and signal quality (e.g., SNIR).

Moreover, at time T6, the small cell may receive an activation grant.The activation grant may include updated downlink transmissionparameters. The RRM server may determine that a group of small cellshave detected the same UE. Thus, the RRM server may transmit activationrequest information to other RRM servers associated with neighboringdonor eNodeBs to coordinate activation grants. Alternatively one RRMserver may be associated with multiple donor eNodeBs, and therefore, theRRM server may not coordinate with other RRM servers.

In another configuration, at time T7, the small cell may autonomouslyproceed to the activation process. Specifically, the small cell mayautonomously proceed to the activation process if the activationcriteria configured at time T1 is met. Furthermore, at time T7, thesmall cell may change its periodicity and offset. For example, theoffset may be changed to O_tf_3 and the periodicity may be anon-infinite value. That is, based on the non-infinite periodicity, thesmall cell may have downlink activity.

FIG. 11 illustrates a method 1100 for activating a small cell. In block1102, a base station configures a small cell with activation parameters.The activation parameters can include a reduced periodicity, as with anew carrier type. The base station configures a UE with time restrictedmeasurements in block 1104. The time restricted measurements maycorrespond to the new carrier type and the reduced periodicity.Furthermore, in block 1106, the base station receives small cell signalmeasurements from the UE. Finally, in block 1108 the base stationinitiates an activation sequence in response to the small cell signalmeasurements.

In one configuration, the eNodeB 610 is configured for wirelesscommunication including means for configuring. In one aspect, theconfiguring means may include the controller/processor 675, memory 676,transmit processor 616, modulators 618, and/or antenna 620, configuredto perform the functions recited by the configuring means. The eNodeB610 is also configured to include a means for receiving. In one aspect,the receiving means may include the receive processor 670, demodulators618, controller/processor 675 and/or antenna 620 configured to performthe functions recited by the receiving means. The eNodeB 610 is alsoconfigured to include a means for initiating. In one aspect, theinitiating means may include the controller/processor 675, memory 676,transmit processor 616, modulators 618, and/or antenna 620 configured toperform the functions recited by the initiating means. In anotheraspect, the aforementioned means may be any module or any apparatusconfigured to perform the functions recited by the aforementioned means.

FIG. 12 is a diagram illustrating an example of an implementation (e.g.,a hardware implementation) for an apparatus 1200 employing a processingsystem 1214. The processing system 1214 may be implemented with a busarchitecture, represented generally by the bus 1224. The bus 1224 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 1214 and the overalldesign constraints. The bus 1224 links together various modules/circuitsincluding one or more processors and/or modules (e.g., hardwaremodules), represented by the processor 1222, the modules 1202, 1204,1206, and the computer-readable medium 1226. The bus 1224 may also linkvarious other modules/circuits such as timing sources, peripherals,voltage regulators, and power management circuits, which are well knownin the art, and therefore, will not be described any further.

The apparatus includes a processing system 1214 coupled to a transceiver1230. The transceiver 1230 is coupled to one or more antennas 1220. Thetransceiver 1230 enables communicating with various other apparatus overa transmission medium. The processing system 1214 includes a processor1222 coupled to a computer-readable medium 1226. The processor 1222 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium 1226. The software, when executedby the processor 1222, causes the processing system 1214 to perform thevarious functions described for any particular apparatus. Thecomputer-readable medium 1226 may also be used for storing data that ismanipulated by the processor 1222 when executing software.

The processing system 1214 includes a configuring module 1202 forconfiguring a small cell with activation parameters, the activationparameters including a reduced periodicity, such as with a new carriertype. The configuring module 1202 may also configure a UE with timerestricted measurements, the time restricted measurements correspondingto the new carrier type and the reduced periodicity. The processingsystem 1214 also includes a receiving module 1204 for receiving smallcell signal measurements from the UE. The processing system 1214 mayfurther include an activating module 1206 for initiating an activationsequence in response to the small cell signal measurements. The modulesmay be software modules running in the processor 1222, resident/storedin the computer-readable medium 1226, one or more hardware modulescoupled to the processor 1222, or some combination thereof. Theprocessing system 1214 may be a component of the eNodeB 610 and mayinclude the memory 676, and/or the controller/processor 675.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as hardware,software, or a combination thereof. To clearly illustrate thisinterchangeability of hardware and software, various illustrativecomponents, blocks, modules, circuits, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination thereof. A softwaremodule may reside in RAM memory, flash memory, ROM memory, EPROM memory,EEPROM memory, PCM (phase change memory), registers, hard disk, aremovable disk, a CD-ROM, or any other form of storage medium known inthe art. An exemplary storage medium is coupled to the processor suchthat the processor can read information from, and write information to,the storage medium. In the alternative, the storage medium may beintegral to the processor. The processor and the storage medium mayreside in an ASIC. The ASIC may reside in a user terminal. In thealternative, the processor and the storage medium may reside as discretecomponents in a user terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software, or combinations thereof. Ifimplemented in software, the functions may be stored, encoded as one ormore instructions or code, or transmitted over as one or moreinstructions or code on a computer-readable medium. Computer-readablemedia includes both computer storage media and communication mediaincluding any medium that facilitates transfer of a computer programfrom one place to another. A storage media may be any available mediathat can be accessed by a general purpose or special purpose computer.By way of example, and not limitation, such computer-readable media cancomprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage,magnetic disk storage or other magnetic storage devices, or any othermedium that can be used to carry or store desired program code means inthe form of instructions or data structures and that can be accessed bya general-purpose or special-purpose computer, or a general-purpose orspecial-purpose processor. Also, any connection is properly termed acomputer-readable medium. For example, if the software is transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. Disk and disc, as used herein, includes compactdisc (CD), laser disc, optical disc, digital versatile disc (DVD),floppy disk, and Blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method of wireless communication, comprising:receiving, at a user equipment (UE), a downlink control channel orderfrom a base station; transmitting, at the UE in response to the downlinkcontrol channel order, a physical random access channel (PRACH)signature sequence that does not initiate a random access procedure atthe UE or the base station; and receiving, at the UE, downlinktransmissions of a small cell activated in response to the PRACHsignature sequence.
 2. The method of claim 1, further comprisingreceiving a time restricted measurement configuration.
 3. The method ofclaim 2, further comprising measuring the downlink transmissions fromthe small cell according to the time restricted measurementconfiguration.
 4. The method of claim 3, in which the downlinktransmissions comprise reference signals transmitted on ports that aredifferent from ports of the base station.
 5. The method of claim 2, inwhich the time restricted measurement configuration corresponds to a newcarrier type and a reduced periodicity.
 6. An apparatus for wirelesscommunication, the apparatus comprising: means for receiving, at a userequipment (UE), a downlink control channel order from a base station;means for transmitting, at the UE in response to the downlink controlchannel order, a physical random access channel (PRACH) signaturesequence that does not initiate a random access procedure at the UE orthe base station; and means for receiving, at the UE, downlinktransmissions of a small cell activated in response to the PRACHsignature sequence.
 7. The apparatus of claim 6, further comprisingmeans for receiving a time restricted measurement configuration.
 8. Theapparatus of claim 7, further comprising means for measuring thedownlink transmissions from the small cell according to the timerestricted measurement configuration.
 9. The apparatus of claim 8, inwhich the downlink transmissions comprise reference signals transmittedon ports that are different from ports of the base station.
 10. Theapparatus of claim 7, in which the time restricted measurementconfiguration corresponds to a new carrier type and a reducedperiodicity.
 11. An apparatus for wireless communication, the apparatuscomprising: a memory; and at least one processor coupled to the memory,the at least one processor configured: to receive, at a user equipment(UE), a downlink control channel order from a base station; to transmit,at the UE in response to the downlink control channel order, a physicalrandom access channel (PRACH) signature sequence that does not initiatea random access procedure at the UE or the base station; and totransmit, at the UE, downlink transmissions of a small cell activated inresponse to the PRACH signature sequence.
 12. The apparatus of claim 11,in which the at least one processor is further configured to receive atime restricted measurement configuration.
 13. The apparatus of claim12, in which the at least one processor is further configured to measurethe downlink transmissions from the small cell according to the timerestricted measurement configuration.
 14. The apparatus of claim 13, inwhich the downlink transmissions comprise reference signals transmittedon ports that are different from ports of the base station.
 15. Theapparatus of claim 12, in which the time restricted measurementconfiguration corresponds to a new carrier type and a reducedperiodicity.
 16. A non-transitory computer-readable medium havingprogram code recorded thereon for wireless communication, the programcode executed by a processor and comprising: program code to receive, ata user equipment (UE), a downlink control channel order from a basestation; program code to transmit, at the UE in response to the downlinkcontrol channel order, a physical random access channel (PRACH)signature sequence that does not initiate a random access procedure atthe UE or the base station; and program code to transmit, at the UE,downlink transmissions of a small cell activated in response to thePRACH signature sequence.
 17. The apparatus of claim 16, in which theprogram code further comprises program code to receive a time restrictedmeasurement configuration.
 18. The apparatus of claim 17, in which theprogram code further comprises program code to measure the downlinktransmissions from the small cell according to the time restrictedmeasurement configuration.
 19. The apparatus of claim 18, in which thedownlink transmissions comprise reference signals transmitted on portsthat are different from ports of the base station.
 20. The apparatus ofclaim 17, in which the time restricted measurement configurationcorresponds to a new carrier type and a reduced periodicity.